A feeding device for drilling tools with automatic reversal of the feeding speed has become known. With this known arrangement, the shifting over from fast traverse to working speed when the tool impacts upon the workpiece is effected in conformity with the increase of the torque or in conformity with the feeding pressure.
There has furthermore become known a deep hole drilling machine with control means controlling the changeover from "fast traverse forward" to "slow speed forward", according to which the tool carrier is, against the thrust of an axially effective spring, caused to engage an abutment of the displaceable tool carriage when the tool hits the workpiece. As control means in this connection there are employed an actuating cam which is coaxially arranged with the tool spindle, and furthermore a tool carriage cooperating with a limit switch cooperating with said actuating cam. Therefore, during the drilling operation, the tool carriage has to be adjusted with the tool carrier.
Furthermore, drilling devices have become known in which the drilling spindle is rotatable in a longitudinally displaceable spindle sleeve while the spindle sleeve is adapted through the intervention of complicated transmission means to be subjected to a faster and a lower rate of feed or advance.
The above mentioned devices have the drawback that either during the drilling operation, also the carriage has to be moved, or expensive transmissions have to be employed, or the duration of the fast traverse relative to the slow speed has to be adjusted in conformity with the distance of the spindle in its starting position from the workpiece of varying sizes. With horizontal drilling and milling machines and so-called machining centers, care is taken that the distance of the workpiece from the spindle in the starting position thereof is as constant as possible. This will be obtained by chucking the workpiece on the turntable of the boring mill or the machining center. With flights of drilling machines with which the device according to the invention may be employed, this aligning of the workpiece which in frequent instances represents a long profiled iron is not possible because the feeding roller bed of such flights determines the position of the workpiece which is held stationary.